Mechanism of Plasma Nitridation of Silicon Dioxide Employing Surface-Wave and Inductively Coupled Plasma Sources

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A thin silicon dioxide (SiO2) film was nitrided with nitrogen plasma generated through a surface-wave plasma (SWP) or inductively coupled plasma (ICP) source. The plasma and nitridation characteristics were compared in both plasma sources. We found that large amounts of nitrogen atomic ions (N+) and neutral radicals (N•) were included in the SWP; however, the dominant species were nitrogen molecular ions (N2+) in the ICP. Nitrogen areal density in the nitrided SiO2 film is correlated with ion dose in the SWP, which suggests that the main reactants are ions. Also, there exists a large nitrogen loss in the ICP, but a small loss in the SWP. To understand these differences, we performed molecular dynamics (MD) simulations based on a semi-empirical molecular orbital (MO) method. We investigated reactions by irradiating N+ or N2+ to a SiO2 molecule, thermal stability of the reaction products, and reactions between the reaction products and N•. Consequently, we found that the reaction products are stable for N+, but are unstable for N2+, which is consistent qualitatively with experimental results. Finally, we conclude that stable reaction products are formed by N+ and N• irradiation, and that the SWP source that we employed is the appropriate plasma source for generating these species efficiently.
2007-08-15